i think that engineers should be the leaders of the gunnery age. as such, i think that the army's handgunners, pistoliers and outriders should benefit from the number of engineers in an army. the engineers take time before battle to train these units extra hard with black powder weapons. the more engineers, the more benefits the army can get. something along these lines...
1 engineer- all handgunner units are armed with bayonets (+1 strength in combat), captains can be given weapons from the engineer's guild (hochland long rifel, ect.)
2 engineers- black powder units no longer suffer the -1 penalty from stand and shoot
3 engineers- handgunners can move and fire. war machine crews are given a pair of pistols each.
4 engineers- all units equipped with black powder weapons have +1 to their ballistic skill.
10 engineers- great cannons and mortars can fire twice in the same turn as long as the fire at the same target with each shot. all units equipped with black powder weapons can shoot twice
as long as the don't move and fire at the same target.
i like this idea because it make the thought of an all engineer army not so bad. who needs magic and awsome warriors when you've got an army that has a chance to blow everything out of the water!
any suggestions would be welcomed but id really like to see this in the next book